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Primer Bulb Not Filling: 7 Ways To Fix It (2023 Guide)

Primer Bulb Not Filling

All of a sudden, your engine won’t start.

You can also feel that the primer bulb isn’t filling.

Even after you pressed it so many times.

So, what may have caused this?

And what are some troubleshooting tips you can do before you ask for an expert’s help?

Keep reading to learn:

  • Easy steps on how to clean your carburetor.
  • Ways to determine the cause of this bulb issue.
  • The reason why your primer bulb stops filling with gas.
  • 7 helpful tips that you can do at home to fix this problem.
  • And so much more…

Why won’t my Primer bulb fill with gas?

Your primer bulb won’t be filled with gas because it might be damaged. This could also be due to switched or deteriorated fuel lines. The hoses or the carburetor may be clogged as well. But sometimes, the other reasons are faulty check valves and ring seals. As well as loose fuel line connections.

Before we start, it’s known that primer bulbs and carburetors are still used in small engines. Say, string trimmers, leaf blowers, and lawnmowers.

Now, some of them may have a 2-cycle or 4-cycle engine. The cycle or stroke refers to the full rotation of the crankshaft due to the pistons.

(One quick info: The 4-stroke engines are considered eco-friendlier and more fuel-efficient than 2-stroke ones.)

This is why primer bulbs also come in different sizes. Depending on the type of equipment you’re using.

However, they still have the same purpose. And it’s to load fuel into the carburetor for combustion.

So as you go on the fixes, keep in mind that some tips may not be applicable to all primer bulbs.

Primer bulb not filling: 9 ways to fix it

#1: Switch the fuel lines

First, have you changed your fuel lines recently?

If so, it might be that they got mixed up. (If not, skip this tip.) 

This is a usual scenario in 2-cycle engines. 

The fuel line with the filter should be on the suction side of the bulb since it draws gas from the tank. 

While the other one must be on the discharge side to return excess fuel.

Now, if the lines were reversed, the primer bulb won’t be filled. This is because the intake line can’t draw fuel from the tank. 

If this is the case, don’t worry. 

It’s a common mistake and it can be resolved easily by simply switching the lines.

But first, check your fuel lines if they’re swapped or not.


Option #1:

  1. Press the primer bulb.
  2. Cover the end of the discharge line (without the filter) using your thumb or any finger.
  3. Release the primer bulb.
  4. Repeat for a few times.

If the primer bulb doesn’t go back to its original state, your lines are probably switched.

Option #2:

  1. Detach your carburetor with the primer bulb.
  2. Prepare a container with fuel.
  3. Soak the 2 lines in it.
  4. Press the primer bulb.

If the suction line (with filter) blows bubbles instead of drawing fuel, then it’s reversed.

#2: Check your lines’ connections and secure them

Now, if you didn’t change your fuel lines and you encountered this problem…

It’s best to check your connections first.

Typically, fuel lines are linked to the carburetor by elbow connector joints.

But for bigger engines, hoses are also secured with clamps. And these could become loose over time.

Either due to accidents. As well as heat expansion.

So, inspect all your connections to see if there are any loose lines.

But if your fuel hoses are old, it’s possible that they’re already damaged.

Over time, they become brittle. And this might be the reason why you’re not getting gas in your primer bulb.

So if this is your case…

#3: Replace your fuel lines

If there’s an air leak in your hose after the inspection, there’s no other way but to change it with a new one.

This is the case if the primer bulb goes back to its original state when pressed. But it doesn’t get filled no matter what.

Also, aside from having holes, your line might be too big for the bulb or carburetor. And this mismatch can also cause leakage.

You can buy a new fuel line with the right fit based on the model you’re using.

Local hardware stores could help you with this. But you may also find some on Amazon.

Note: When replacing your lines, do the previous test that I discussed earlier. Then take note of the bulb’s direction of flow. Do this to avoid the reversal of lines.

Also, to insert the lines easier, cut their ends at a sharp angle.

#4: Clean the carburetor

Your lines and primer bulb are working just fine.

What could be the problem?

Well, the carburetor might be the culprit for this.

Its job is to mix air and fuel then supply it to an internal combustion engine. So this can get dirty and clogged in the long run.

“How can I clean it?”

First, you have to buy a carburetor cleaner.

There are many kinds available in the market. So it’ll help if the manufacturer has recommended one.

And then, now that you have your tools:

Remove the carburetor

  1. Detach the cover of your equipment.
  2. Remove the screws that hold the air filter in place.
  3. Disconnect the fuel line from the carburetor. (Place a container or an old towel under the area to absorb residual fuel.)
  4. Detach the carburetor from the engine. And safely unfasten any linked cables.

Cleaning time

This is for float-type carburetors.

  1. Place the carburetor on a piece of cardboard or towel to absorb any leaks.
  2. Wear gloves and safety glasses. (The cleaner and dirt might get into your eyes while brushing the parts.)
  3. Using a ½” socket and ¼” ratchet (or as needed), remove the bowl nut. This is to detach the fuel bowl from the carburetor body.
  4. Take off the other parts as well. Like the float, fuel bowl gasket, valve, and other screws. But take note and list down of their placements.
  5. Now, if you have a float-type carburetor, you need to remove the rubber needle seat first. (You can do this using a Tecumseh tool or a crochet hook of the same size.)
  6. Then, spray a generous amount of cleaner to the carb. As well as to its other metal parts.
  7. You can also get a container with carb cleaner. Then submerge the parts in it.
  8. Let them soak for at least 30 minutes to 1 hour.
  9. Drain the carb cleaner and wipe each part.
  10. Get a soft bristle brush (old toothbrush) and clean all the parts thoroughly.
  11. Clean all the tiny holes using tip cleaner tools.
  12. Use compressed air to blow out all the fuel and air passages.
  13. Wipe everything until it’s clean and dry.
  14. Reattach all the small parts one by one. (From the rubber needle seat, float, fuel bowl, etc.)
  15. After assembling, reconnect the throttle cable to the carburetor. And secure it back to its place.
  16. Link all the fuel lines again. (Ensure that every all joints are tight and secured.)
  17. Reinstall the air filter and cover.

And you’re done.

If you want to see a more detailed tutorial, check out this video:

Note: Use soft brushes to avoid scratches. Also, be careful when blowing out the passages. There might be small rubber seats at the bottom.

Sometimes, all our equipment need is a thorough cleaning.

Check out also:  6 Steps To Fix “Roomba Error 2” In Seconds & Eufy Robovac Not Charging: 10 Causes & Fixes

#5: Inspect the bulb and do a simple remedy

Are you sure that all your lines and connections are fine?

If so, inspect your primer bulb next.

In some equipment, this is placed directly on the carburetor. While in other engines, it’s only connected to it by a fuel line.

Now, take a closer look at your bulb. Check for any holes or cracks.

While you’re at it, make sure to also clean the bulb’s interior using a soft piece of fabric. As well as its plate as there could be a build-up of dirt underneath it.

Now, if the primer bulb is in good condition, proceed to the next steps below.

But if you have a broken or cracked one, here’s an easy short-term solution that you can do:

  1. Get a plastic bag.
  2. Cut a piece of it – about 2” x 2” in size. (This is enough for most 2-cycle engines.)
  3. Remove the screws that hold the primer bulb.
  4. Detach the bulb from its metal retainer.
  5. Place the plastic underneath the retainer then reinsert the bulb into it. (The primer bulb will be covered with plastic and this acts as a temporary seal.)
  6. Put the bulb and retainer back to the engine.

Note: This is only temporary so the seal won’t last long. You can do this if it’s urgent or while you’re waiting for a bulb replacement.

#6: Buy a new primer bulb

Next, the remedy above is only short-term. So if you have a broken primer bulb, look for a replacement at once.

Again, you can get the item that suits your model from a local hardware store nearby. As well as in Amazon.

Now, if you already have a new primer bulb kit, here’s how you can change it.

I’ll discuss 2 ways since it’ll be different based on your equipment. 

But take note, there still might be some discrepancies in the steps. So check your owner’s manual as well for verification.

Removing the primer bulb

  1. Detach the cover of your equipment first (if needed).
  2. Remove the screws that hold your carburetor.
  3. Take out the carburetor carefully.
  4. Unfasten it from the throttle cable.
  5. Drain all the gas inside before removing any connection.
  6. Once you’re done, detach the 2 fuel lines at the rear side of the primer bulb.

But again, remember their placement. Usually, it’s like this:

  • Shorter nipple: Suction line (between the primer and the carburetor).
  • Longer nipple: Discharge/return line (between the primer and fuel tank).
  1. Then remove the primer bulb from the base. (Gently squeeze the 2 tabs that hold it in place to do this.)

Installing the new primer bulb

  1. Get the new bulb. 
  2. Check the tabs of the slot. (Normally, bulbs will only fit one way for security. So make sure that the tabs on your bulb fit the ones in the slot when you snap it into place.)
  3. Kits may include both the bulb and a short fuel line. So replace your old one that connects the primer and the carburetor.
  4. Then link the short fuel line to the shorter nipple of the primer bulb.
  5. Reconnect the longer/return line as well to the longer nipple.
  6. Reattach the throttle cable to your carburetor.
  7. Secure the carburetor with its chokeplate. And reinstall its screws.
  8. Place the cover back on your equipment.

Now, some equipment may not require you to remove the whole carburetor.

You only have to:

  1. Search for the primer bulb once the cover is removed.
  2. Detach the primer bulb plate by removing its screws.
  3. Take out the old bulb from it.
  4. Insert the new one into the bulb plate.
  5. Reinstall the bulb plate to the engine.
  6. Rettach the cover. 

Then that’s it.

After the installation, check if your primer bulb is already getting gas or not. 

#7: Examine and clean its check valve

Examine And Clean Primer Check Valve

If you remove the primer bulb, you’ll see a reddish rubber disk under it.

It’s called a ‘check valve’ and its job is to prevent reverse flow.

Meaning, it only allows fluids and gases to move in a single direction.

For example, once the fuel goes through it, it can’t go back to where it came from. So think of it as a gate that only allows either entry or exit of p.

Now, like the other parts, a check valve can also be clogged or damaged.

If it’s the former, the dirt can be removed using a carburetor cleaner. 

But if it’s the latter, it needs to be changed.

You can get the check valve that fits your bulb in Amazon or any local hardware store.

“How will I know if there’s a problem with my check valve?”

If this happens, the primer bulb won’t be filled with fuel. 

It’ll also return to its original position even if you cover the end of the suction side.


The check valve is impaired so it lets gases in and out. Instead of preventing them from going back to the bulb.

#BONUS: Change the O-Rings

Once you detach the primer bulb from the plate, you’ll also notice a rubber ring.

Typically, it’s placed in grooved parts to avoid any leak of gas or fluids.

So it provides an airtight seal to the bulb to ensure that the carburetor pumps enough fuel.

It’s called an O-Ring and it can wear out too. So it’s best to check its condition as well, along with the check valve. 

Then replace it with a new one if it’s already defective.

Note: If none of the tips above work, you might have a bigger issue. And you need help from an experienced mechanic.